1. Field of the Invention
This invention is directed to methods and apparatuses for treating the pharyngeal wall of a patient. More particularly, this invention pertains to method and apparatus for treating a pharyngeal wall area as part of a sleep apnea treatment.
2. Description of the Prior Art
Sleep apnea and snoring are complex phenomena. Commonly assigned U.S. Pat. No. 6,250,307 describes various prior techniques and discloses a novel treatment for such conditions (including a permanent palatal implant).
These prior art teachings include Huang, et al., “Biomechanics of Snoring”, Endeavour, p. 96–100, Vol. 19, No. 3 (1995). That publication estimates that up to 20% of the adult population snores habitually. Snoring can be a serious cause of marital discord. In addition, snoring can present a serious health risk to the snorer. In 10% of habitual snorers, collapse of the airway during sleep can lead to obstructive sleep apnea syndrome. Id. In addition to describing a model for palatal flutter, that publication also describes a model for collapse of the pharyngeal wall.
Notwithstanding efforts have been made to treat snoring and sleep apnea. These include palatal treatments such as electrical stimulation of the soft palate. See, e.g., Schwartz, et al., “Effects of electrical stimulation to the soft palate on snoring and obstructive sleep apnea”, J. Prosthetic Dentistry, pp. 273–281 (1996). Devices to apply such stimulation are described in U.S. Pat. Nos. 5,284,161 and 5,792,067. Such devices are appliances requiring patient adherence to a regimen of use as well as subjecting the patient to discomfort during sleep. Electrical stimulation to treat sleep apnea is discussed in Wiltfang, et al., “First results on daytime submandibular electrostimulation of suprahyoidal muscles to prevent night-time hypopharyngeal collapse in obstructive sleep apnea syndrome”, International Journal of Oral & Maxillofacial Surgery, pp. 21–25 (1999).
Surgical treatments for the soft palate have also been employed. One such treatment is uvulopalatopharyngoplasty (UPPP) where about 2 cm of the trailing edge of the soft palate is removed to reduce the soft palate's ability to flutter between the tongue and the pharyngeal wall of the throat. See, Huang, et al., supra at 99 and Harries, et al., “The Surgical treatment of snoring”, Journal of Laryngology and Otology, pp. 1105–1106 (1996) which describes removal of up to 1.5 cm of the soft palate. Assessment of snoring treatment is discussed in Cole, et al., “Snoring: A review and a Reassessment”, Journal of Otolaryngology, pp. 303–306 (1995). Huang, et al., propose an alternative to UPPP which proposal includes using a surgical laser to create scar tissue on the surface of the soft palate. The scar is to reduce flexibility of the soft palate to reduce palatal flutter. RF ablation (so-called Somnoplasty as advocated by Somnus Technologies) is also suggested to treat the soft palate. RF ablation has also been suggested for ablation of the tongue base.
In pharyngeal snoring and sleep apnea, the pharyngeal airway collapses in an area between the soft palate and the larynx. One technique for treating airway collapse is continuous positive airway pressure (CPAP). In CPAP air is passed under pressure to maintain a patent airway. However, such equipment is bulky, expensive and generally restricted to patients with obstructive sleep apnea severe enough to threaten general health. Huang, et al. at p. 97.
Treatments of the pharyngeal wall include electrical stimulation is suggested in U.S. Pat. No. 6,240,316 to Richmond et al. issued May 29, 2001, U.S. Pat. No. 4,830,008 to Meer issued May 16, 1989, U.S. Pat. No. 5,158,080 to Kallok issued Oct. 27, 1992, U.S. Pat. No. 5,591,216 to Testerman et al. issued Jan. 7, 1997 and PCT International Publication No. WO 01/23039 published Apr. 5, 2001 (on PCT International Application No. PCT/US00/26616 filed Sep. 28, 2000 with priority to U.S. Ser. No. 09/409,018 filed Sep. 29, 1999). U.S. Pat. No. 5,979,456 to Magovern dated Nov. 9, 1999 teaches an apparatus for modifying the shape of a pharynx. These teachings include a shape-memory structure having an activated shape and a quiescent shape. Dreher et al., “Influence of nasal obstruction on sleep-associated breathing disorders”, So. Laryngo-Rhino-Otologie, pp. 313–317 (June 1999), suggests using nasal stents to treat sleep associated breathing disorders involving nasal obstruction. Upper airway dilating drug treatment is suggested in Aboubakr, et al., “Long-term facilitation in obstructive sleep apnea patients during NREM sleep”, J. Applied Physiology, pp. 2751–2757 (December 2001).
Surgical treatments for sleep apnea are described in Sher et al., “The Efficacy of Surgical Modifications of the Upper Airway in Adults with Obstructive Sleep Apnea Syndrome”, Sleep, Vol. 19, No. 2, pp. 156–177 (1996). Anatomical evaluation of patients with sleep apnea or other sleep disordered breathing are described in Schwab, et al., “Upper Airway and Soft Tissue Anatomy in Normal Subjects and Patients with Sleep-Disordered Breathing”, Am. J. Respir. Crit. Care Med., Vol. 152, pp. 1673–1689 (1995) (“Schwab I”) and Schwab et al., “Dynamic Upper Airway Imaging During Awake Respiration in Normal Subjects and Patients with Sleep Disordered Breathing”, Am. Rev. Respir. Dis., Vol. 148, pp. 1385–1400 (1993) (“Schwab II). In Schwab I, it is noted that apneic patients have a smaller airway size and width and a thicker lateral pharyngeal wall. For reviews of pharyngeal wall thickness and other structure and obstructive sleep apnea, see, also, Wheatley, et al., “Mechanical Properties of the Upper Airway”, Current Opinion in Pulmonary Medicine, pp. 363–369 (November 1998); Schwartz et al., “Pharyngeal airway obstruction in obstructive sleep apnea: pathophysiology and clinical implication”, Otolaryngologic Clinics of N. Amer., pp. 911–918 (December 1998); Collard, et al., “Why should we enlarge the pharynx in obstructive sleep apnea?”, Sleep, (9 Suppl.) pp. S85–S87 (November 1996); Winter, et al., “Enlargement of the lateral pharyngeal fat pad space in pigs increases upper airway resistance”, J. Applied Physiology, pp. 726–731 (September 1995); and Stauffer, et al., “Pharyngeal Size and Resistance in Obstructive Sleep Apnea”, Amer. Review of Respiratory Disease, pp. 623–627 (September 1987).
There are contrasting opinions in the medical literature on the mechanisms of OSA. OSA patients are a heterogeneous group; there are differing locations and patterns of pharyngeal collapse for each person. In addition to the physical findings and properties which characterize the pharynx in patients with OSA such as increased collapsibility, increased compliance, increased resistance, and decreased cross-sectional area, the physical properties and spatial relationships of the pharyngeal airway, head, and neck, as well as the neuromuscular integrity of the airway (reflexes affecting upper airway caliber) and mechanisms of breathing control (pharyngeal inspiratory muscle function) must also be considered relevant in their contribution to the mechanism and precipitation of upper airway collapse. Hudgel D W, Mechanisms of Obstructive Sleep Apnea. Chest 1992; 101:541–49. Fairbanks DNF, Fujita S, Snoring and Obstructive Sleep Apnea. Raven Press Ltd., New York, 1994.
In general, obstructive apnea occurs during sleep, when the pharyngeal dilator muscle activity (genioglossus, tensor palatini, geniohyoid, stylohyoid) that normally maintains airway patency during inspiration through dilation of the airway, is diminished. (Fairbanks DNF, Fujita S, Snoring and Obstructive Sleep Apnea. Raven Press Ltd., New York, 1994.2, p. 85). When the intraluminal negative pressure of the airway reaches a critical point, the combination of redundant tissues and the loss of pharyngeal muscle tone causes airway collapse during inspiration. Please note, obstruction has been shown to occur during expiration and inspiration (Schwab R J et al., Dynamic imaging of the upper airway during respiration in normal subjects. J Appl Physiol 1993; 74(4):1504–1514. Schwab R J, Functional Properties of the Pharyngeal Airway. Sleep 1996; 19(10):S170–S174. 8, 9); details on how upper airway area changes during the respiratory cycle can be found in the cited literature. Surgical treatments are aimed at eliminating any collapsible tissue in the airway and reducing airway resistance without creating functional impairment of the upper airway structures.